High strength catalyst pellets

ABSTRACT

A method of preparing a high strength catalyst pellet is disclosed which comprises calcining particulate ZnO admixed with particulate Al2O3. Additionally, a catalytic process using a prepared high strength catalyst is disclosed.

O Unlted States Patent [151 3,668,151

Walker 1 June 6, 1972 54] HIGH STRENGTH CATALYST PELLETS 2,269,508 11942 Barton ..23 52 3,470,262 9/1969 Michaels... ..260/680 [72]Inventor. Darrell W. Walker, Banlesville, Okla. 3,461,183 8/1969 Heppm260/680 [73] Assignee: Phillips Petroleum Company 3,461,177 8/1969 BOX 73,502,739 3/1970 Begley ..260/680 [221 May 1969 3,511,883 5 1970 Jenkins..260/673.5

[21] Appl. No.: 828,772

Primary Examiner-Damel E. Wyman Assistant Examiner-Philip M. French [52]U.S. Cl... ..252/466, 252/463, 23/52 A[t0rneyYQung d Quigg [51] Int. Cl...BOlj 11/22 [58] Field of Search ..260/680, 683.3; 252/466, 463; [57]ABSTRACT l A method of preparing a high strength catalyst pellet is dis-56 closed which comprises calcining particulate ZnO admixed 1 ReferencesCited with particulate A1 0 Additionally, a catalytic process usingUNlTED STATES PATENTS a prepared high strength catalyst is disclosed.

3,531,543 9/1970 Clippinger ..260/683.3 4 Claims, No Drawings HIGHSTRENGTH CATALYST PELLETS This invention relates to a method ofpreparing high strength zinc aluminate catalyst. In another aspect thisinvention relates to a process for using the prepared zinc aluminate asa catalyst.

In recent years catalytic reactions have assumed great industrialimportance. In many of these catalytic reactions the catalyst isdesigned to exist in discrete forms or pellets. A problem exists whenthe pellets break up into smaller fragments during the catalyticprocess. Upon breaking up, or fragmenting, of the pellets the smallerparticles can plug the catalytic reactor itself such as when smallerfragments fill up the catalyst support screen in a fixed bed reactor, orthe smaller particles can escape from the catalyst retention area andcontaminate downstream equipment and products. Thus, it is highlydesirable to eliminate catalyst pellet fragmentation in catalyticreactors.

One embodiment of this invention comprises a high strength catalystpellet made by calcining particulate ZnO admixed with particulate Ago,Another embodiment of this invention comprises a catalytic process usingthe prepared high strength catalyst.

Accordingly, it is an object of this invention to prepare a highstrength catalyst pellet. Additionally, it is an object of thisinvention to conduct a catalytic reaction utilizing a high strengthcatalyst pellet. Furthermore, it is an object of this invention toreduce the operating costs of a catalytic reaction by eliminatingdownstream cleanup or reactor fouling due to catalyst pelletfragmentation. In addition, it is an object of this invention tominimize off-specification product by retaining catalyst in the catalystretention area. Other objects, advantages and features of this inventionwill be readily apparent to those skilled in the art from the followingdescription and appended claims.

The particulate ZnO useful with this invention can comprise anyparticulate ZnO having an average particle diameter in the range fromabout 0.l-l,000 microns; however, entirely satisfactory results areobtained when the ZnO average particle diameter is in the range of about40-900 microns and in a preferred embodiment an average particlediameter of about 300 microns is used.

The M used in this invention can comprise any flamehydrolyzed Al Owherein the average particle diameter is in the range from about 0.01-1micron. Additionally, satisfactory results are obtained when the Al O isin the range from about 0.025-0.75 micron average particle diameter andparticularly satisfactory results are achieved when the average particlediameter is 0.03 micron. Thus, according to this invention, the termflame-hydrolyzed refers to an A1 0 made by the hydrolysis of aluminumchloride in the flame process such as A1 0 sold commercially by theCabot Corporation, Boston, Mass, under the trademark ALON said ALONcomprising a mixture of different crystalline forms of alumina, saidalumina being predominantly of the gamma modification.

According to the invention, the particulate ZnO and particulate A1 0 areinitially mixed together. The ratio of ZnO to A1 0 can be in the molarrange from 1 /0.7-1/ 1.1 and in one embodiment about 0.52 mol of ZnO wasadmixed with about 0.50 mol of A1 0 According to this invention, the twoparticulate materials can be mixed in any manner that will insuresatisfactory admixing, specifically, a ball mixer or a ball mill can beused. In one embodiment deionized water was used to facilitate admix- Inone embodiment of the invention, the particulate ZnO- A1 0 mixture isdried prior to pelletizing. Any drying technique that will result in asufficiently dry product to be useful in this invention is satisfactory;however, in one embodiment, the deionized water used as a wetting agentwas removed by drying at 100 C. for 16 hours.

According to this invention, the admixture is pelletized according toany manner convenient to the user. If desired, various lubricants andother pelletizing additives may be added.

The pellets of this invention are calcined for a sufficient time and ata sufficient temperature to result in a pellet of high strength. In oneembodiment, the pelletized admixture can be calcined from about 0.1-30hours at a temperature in the range from about 600-l,500 C., while inanother embodiment, the pelletized admixture was calcined from about l30hours at a temperature from about SOU -1,200? C. In an additionalembodiment, the pellets can be calcined at about l,OO0 C. for about 16hours.

The catalyst pellets of this invention can be used directly as acatalyst after calcining or can be impregnated with other materials andused as a catalyst. Any suitable catalyst can be used to impregnate thecalcined pellet. Specifically, a metal catalyst can be used and, morespecifically, satisfactory results are obtained when the calcined pelletis impregnated with a metal selected from the group consisting ofplatinum, lithium, and tin and mixtures thereof. In one embodiment,impregnation was accomplished by sufficient aqueous solution to resultin the impregnated pellet containing, based on the weight of theimpregnated pellet, about 0.25 weight per cent platinum, about 0.25weight per cent lithium, and about 0.15 weight per cent tin.

After the calcined pellets have been impregnated, if desired, they canbe dried. Any drying which will result in successful operation of theinvention is satisfactory.

Thus, according tothis invention, the basic steps are combiningparticulate ZnO and particulate A1 0 pelletizing the admixture, andcalcining the pellets. Obviously, many other steps are fully within thescope of this invention, some of which are noted specifically, such asadmixing the particulate materials in the presence of water or othersuitable lubricant, drying the admixed product, impregnating the pelletswith an additional catalyst, drying the impregnated pellets, and thelike.

According to this invention, the calcined products can be used in anycatalytic reaction where the calcined pellets catalyze conversion.Specifically, the catalysts of this invention, both unimpregnated andimpregnated with additional catalyst materials, are useful for thedehydrogenation of hydrocarbons and, more specifically, for thedehydrogenation of n-butane to olefins and diolefins. The catalyticreaction conditions can comprise any conditions that will result in theproduct desired with the selected feedstock. In the specific embodimentwhere n-butane is converted to olefins and diolefins, 635 C. and psigwere found to be entirely satisfactory.

Thus, according to this invention, a high strength catalyst pellet isproduced. The term high strength means a pellet of the catalyticmaterial described in this application which exhibits resistance tocrushing. A convenient method of testing a crushable discrete particlefor resistance to crushing is to utilize the device disclosed in US.Pat. No. 2,976,723 to Eddy on Mar. 28, 1961, herein incorporated byreference, wherein a pellet is placed between two tangentially impingingsurfaces and the force in pounds necessary to crush the pellet ismeasured. According to this invention, the term high strength indicatesa pellet tested according to the following apparatus exhibiting a crushstrength in excess of 15 pounds, although higher crush strengths arefully within the scope of this invention and, in fact, crush strengthsin excess of 25 pounds are demonstrated in the appended examples.

EXAMPLE I In order to demonstrate the preparation of a catalyst notexhibiting the high strength character of this invention, 3,981 grams ofa hydrated zinc nitrate was admixed with 10,228 grams of a hydratedaluminum nitrate in 50 gallons of deionized water. Concentrated ammoniawater (28 weight per cent NI-I was added with stirring to a pH of 7 toprecipitate an intimate mixture of the corresponding hydroxides. Theprecipitate was filtered, washed, and spray dried to a fine powder. Thespray dried powder was tableted, calcined 12 hours at 1,250 C., andtested for crush strength by utilizing the apparatus disclosed in U.S.Pat. No. 2,976,723 and found to be within the range from 5 to 8 pounds.The pellets were then crushed to 20-40 mesh and impregnated withsufficient aqueous solution to result in the impregnated pelletcontaining, .based on the weight of the impregnated pellet, 0.25 .weightper cent platinum, 0.25 weight per cent lithium, and 0.15 weight percent tin. The pellets were dried and tested for catalyticdehydrogenation activity at about l,050 F. by introduction into alaboratory catalytic reactor operating at conditions of 1,235 'v/v/hoursnormal butane feed, and 5,680 v/v/hours steam at 85 psig. The results ofthe catalytic conversion are given'in Table I.

TABLE I Conversion,

weight per cent EXAMPLE II The practice of the invention wasdemonstrated by taking 0.52 mol of particulate ZnO with an averageparticle diameter of about300 microns and admixing in a dry manner with0.50 mol of flame-hydrolyzed ALON A1 0 wherein the particle diameter wasabout 0.03 micron. The dry admixture was wet with 100 ml of deionizedwater, dried, pelleted into Aa-inch pellets, calcined overnight at l,000C. and tested for strength in the same device as used in Example I.Pellet crushing strength was noted to be 26.2 pounds. The pellets werethen impregnated in the same manner as in Example I and tested in thesame catalytic reactorat the same conditions, the results of which aregiven in Table ll. 1

TABLE II Selectivity to Conversion, Olefin and Diolefin weight per centweight per cent 39.9 97.9

Analysis of the results of Table I as compared to Table II indicatesthat the high strength pellet of this invention demonstrated in ExampleII is an entirely suitable catalyst and contains approximately the samecatalytic properties as the conventional low strength catalyst pelletsdemonstrated as a control in Example I. Thus, applicant has demonstratedthat the high strength pellets of this invention are entirelysatisfactory as a catalytic material.

EXAMPLE Ill Additional runs were conducted in which the calcined timewas varied. Specifically, in this example the same materials as inExample II were prepared in pellets in the same manner and calcined atl,000 C In a first run the calcining time was 1 hour and in a second runthe calcining time was 16 hours. The pellets of run one, where thecalcining time was 1 hour, had a crushing strength of 28 pounds whentested in the same device as in Example II, and the pellets of run two,which were subjected to a calcining time of 16 hours, exhibited acrushing strength of 26 pounds in the same device. It is noted that thecatalyst pellets had a remarkably high crushing strength when calcinedunder these conditions.

EXAMPLE IV Additional runs were made in which the calcining temperaturewas varied. Thus, the invention was practiced by preparing pelletsaccording to the manner of Example II and calcining the pellets for 16hours. In a first run the calcining temperature was 800 C. and in asecond run the calcining temperature was l,200 C. The tablets from thefirst run wherein the calcining temperature was 800 C. tested at 28pounds crushing strength, while the tablets of the second run at 1,200C. also tested at 28 pounds. Thus, applicant has demonstrated l. Amethod of preparing a zinc aluminate catalyst having a crush strength ofat least 15 pounds measured by the apparatus of U.S. Pat. No. 2,976,723comprising the steps of:

a. admixing in the ratio of 1. one mol of particulate ZnO, wherein theaverage particle diameter is in the range of 0. l-l ,000 microns, and

2. about 0.7-1.1 mols of particulate flame-hydrolyzed A1 0 said Iflame-hydrolyzed alumina comprising predominately gamma Al O wherein theaverage particle diameter is in the range of about 0.01-1 micom;

b pelletizing the admixture; and v c calcining the pellets at atemperature in the range of 600 to l,500 C. for from 0.1 to 30 hours.

2. The method of claim 1 wherein the particle size of said ZnO is in therange of about 40-900 microns average particle diameter and the particlesize of said flame-hydrolyzed A1 0; is in the range from about0.025-0.75 micron average particle diameter.

3. The method of claim 2 wherein said pelletized admixture is calcinedat a temperature in the range of about 800l ,200" C. for from l-30hours; and

further comprising impregnating said calcined admixture with a metalcatalyst.

4. The method of claim 3 further comprising the steps of:

a. admixing in deionized water in the ratio of:

1. about 0.52 mol of particulate ZnO, wherein said particle size isabout 300 microns average particle diameter; with 2. about 0.50 mol ofparticulate flame-hydrolyzed A1 0 wherein said particle size is about0.03 micron average

2. about 0.7-1.1 mols of particulate flame-hydrolyzed Al2O3, saidflame-hydrolyzed alumina comprising predominately gamma Al2O3, whereinthe average particle diameter is in the range of about 0.01-1 micorn; bpelletizing the admixture; and c calcining the pellets at a temperaturein the range of 600* to 1,500* C. for from 0.1 to 30 hours.
 2. Themethod of claim 1 wherein the particle size of said ZnO is in the rangeof about 40-900 microns average particle diameter and the particle sizeof said flame-hydrolyzed Al2O3 is in the range from about 0.025-0.75micron average particle diameter.
 2. about 0.50 mol of particulateflame-hydrolyzed Al2O3, wherein said particle size is about 0.03 micronaverage particle diameter; b. drying said admixture; c. pelletizing saiddried admixture into pellets; d. calcining said pellets at about 1,000*C. for about 16 hours; e. impregnating the pellets with sufficientaqueous solution to result in the impregnated pellets containing, basedon the weight of the impregnated pellets, about 0.25 weiGht per centplatinum, about 0.25 weight per cent lithium, and about 0.15 weight percent tin; and f. drying said impregnated pellets.
 3. The method of claim2 wherein said pelletized admixture is calcined at a temperature in therange of about 800*-1,200* C. for from 1-30 hours; and furthercomprising impregnating said calcined admixture with a metal catalyst.4. The method of claim 3 further comprising the steps of: a. admixing indeionized water in the ratio of: